Experimental delineation of gas-particle coupling regimes in explosive volcanic eruptions

• Published in: Journal of volcanology and geothermal research 2022-11, Vol.431, p.107654, Article 107654
• Main Authors: Alatorre-Ibargüengoitia, Miguel A., De Arcia, Paulina, Dingwell, Donald B., Ramos-Hernández, Silvia G.
• Format: Article
• Language: English
• Subjects: Experiment; Gas-particle coupling; Pyroclast; Shock-tube; Stokes number; Volcanic eruption
• ISSN: 0377-0273; 1872-6097
• DOI: 10.1016/j.jvolgeores.2022.107654

The kinematic and thermal coupling between pyroclasts and gas is one of the main controlling factors in the dynamics of explosive volcanic eruptions. Here, we performed rapid decompression experiments in a shock-tube apparatus at eruptive pressures (2–11 MPa) using monodisperse volcanic particles (grain-size 0.063–1.4 mm). We systematically investigated the coupling of these particles with the gas phase by measuring the rarefaction speed and the ejection velocity of the particles front in each experiment. The results are consistent with a theoretical model derived from the pseudogas approximation (i.e. perfect coupling) only for particles smaller than a certain size: ∼ 0.125 mm for rarefaction speed and ∼ 0.5 mm for the particles front ejection velocity, whereas larger particles are significantly decoupled. We present an experimental parameterization to calculate the kinematic Stokes number (Stk). We show that: 1) for the ejection process the particles are coupled with the gas if Stk